The subject invention relates to a bladder shell for inflatable balls comprising at least a pair of layers of compounded synthetic latex and compounded natural rubber latex laminated together and crosslinked integrally to each other by vulcanization to form a low air permeability and high bounce bladder shell. The total thickness of the resultant laminated layers is from 0.25 mm to 3.0 mm.
Another embodiment of the invention relates to an improved process for the manufacture of a latex bladder shell for use in inflatable bladder comprising at least a layer of natural rubber latex and synthetic latex each. The main embodiment of the process of the present invention resides in providing lamination of more than one layer of latex to form a bladder with improved properties of air retention as well as bounce characteristics.
The object of the invention is to make a bladder with low air permeability and high bounce properties.
The conventionally available bladders in the market either posses low air permeability property or have the high bounce property. There is always a need for the bladders which are having both the low air permeability and high bounce properties.
In the rubber bladders as known conventionally, rubber compounds such as butyl rubber are compounded on a rubber mill or banbury mixer. This compound is thee calendered to the desired thickness in sheet form. From the rubber sheet, quarter sections of the bladder are die cut and pieced together by hand with adhesive and end patches. A valve is inserted and adhered to the construction. The total construction is then heat cured to produce a bladder. The adhesive application results in the imperfect seals and poor weight balance. This conventional process often results in high amounts of defective bladders and excess scrap.
The bladders made up of thermoplastic materials such as polyethylene powders and vinyl plastisols are also known conventionally. However, these materials are found to have no bounce but have good air retention and hence found not suitable for inflatable bladders.
The inflatable bladders made up of natural rubber are also available conventionally. The latex rubber bladder shell made from natural rubber latex as available in the market are found to have very good bounce property but have high air permeability properties. Due to high air permeability, the air leaks out frequently leading to frequent refilling of the bladder within short durations.
The bladders made up of butyl rubber are also known conventionally. The bladder composition containing low unsaturated butyl rubber has been disclosed in U.S. Pat. No. 4,022,848. This Patent teaches the use of butyl rubber composition in tire curing bladders, air bags and curing tubes.
Butyl rubber is well known in the art and is disclosed in U.S. Pat. No. 3,031,423, column 1, lines 15 to 24. The problems faced with the butyl rubber bladder is that while it has a good air retention, but it lacks in good bounce properties.
Hence, there is a need to decrease the air permeability without affecting the bounce and other properties.
The present invention provides a bladder shell for inflatable ball with desired low air permeability and high bounce characteristics. The invention also defines process for preparation of such bladder shells.
The subject invention relates to a bladder shell for inflatable balls comprising at least a pair of layers of compounded synthetic latex and compounded natural rubber latex laminated together and crosslinked integrally to each other by vulcanization to form a low air permeability and high bounce bladder shell and the total thickness of the resultant laminated layers is from 0.25 mm to 3.0 mm.
The invention also relates to a bladder shell for inflatable balls, comprising at least a layer of blended synthetic latex and natural rubber latex blended in the ratio of 80:20 to 20:80 compounded with anti-oxidant, activators, accelerators, thickening and wetting agents, stabilizers etc. to form a low air permeability and high bounce bladder shell, wherein the total thickness of the compounded laminated layers is from 0.25 mm to 3.0 mm.
To achieve the desired results of low air permeability and high bounce properties, the inflatable bladder shell is processed from the blend of synthetic rubber latex compound and natural rubber latex compound or from laminar dip of more than one compounded lattice.
Latex dipping processes appeared as natural rubber lattices became commercially available in an adequately stable form in the period around 1930s. They followed on as a development of rubber solution dipping as they were less hazardous, more economic and technically more versatile with their high rubber content. Latex dipping process consists of using an inert former, which is in the shape of the ultimately desired product, and this former is coated with one or more dips of the latex compound. The coating is set by a coagulant and/or heat dried into a continuous film which can then be stripped from the former.
The conventionally known processes have used natural rubber latex for the preparation of the bladder shell and the former is dipped into a natural rubber latex where coating is set with one or more coagulant dips. The bladder thus formed exhibits high bounce and low air retention properties.
The present invention relates to a process for the preparation of a bladder which exhibits the desired characteristics of high bounce as well as low air permeability. The main embodiment of the present invention resides in the formation of at least a layer of natural rubber latex and a synthetic latex each. The process of the present invention comprises dipping the former in not only a compounded natural rubber latex bath but also in compounded synthetic latex bath. The former is dipped in compounded natural rubber latex bath and compounded synthetic rubber latex alternatively, in any order, thereby forming two different layers of the latex on the former. The end product when stripped has therefore a combination of components present which not only exhibits the desired bounce characteristic but also the required low air permeability properties. More than one layer of the natural rubber latex and the synthetic rubber latex may also be deposited depending upon the characteristics of the end product required.
In an another embodiment, the coagulant coated former is first dipped into a latex dipping tank comprising synthetic rubber latex and other constituents followed by drying, coagulant coating and then dipping into a bath having natural rubber latex along with other constituents or vice versa.
The various ingredients added to the latex i.e. natural rubber latex and/or synthetic rubber latex are selected from the antioxidants, accelerators, activators, stabilizers, softening agents, fillers, waxes, colours, de-webbing agents and non-foaming surfactants.
These ingredients are added into the latex in the form of solutions, dispersions, or emulsions. The ingredients in the form of dispersions and emulsions are added to lattices to form a compound. After preparing the synthetic and natural rubber compounds, the same are transferred to their respective dipping tanks.
To make a blend of natural rubber latex and synthetic rubber latex, the same are mixed in the ratio of 80:20 to 20:80 with the help of stirrer at the rate of 10-15 RPM and passed through a homogenizer to form a homogeneous mixture.
The bladder shell for inflatable balls comprising at least a pair of layers of natural rubber latex and/or synthetic latex are compounded with
antioxidant from 0.01 to 3 PHR
accelerators from 1 to 3 PHR
activators from 0.01 to 5 PHR
thickening and wetting agents from 0.5-1 PHR
stabilizers from 0.1-2 PHR and optionally
softeners from 0.1-2 PHR and
fillers from 5-20 PHR
The natural rubber lattices are selected from Epoxidised NR latex, Cream latex, Centrifuge latex or double centrifuged latex.
The accelerators are selected from Dithiocarbamate, Vulkacit LDA, Vulkacit LDB, Setsit 9, Setsit 5, Butyl namate, Guanidine, Vulkacit DOTG, Vulkacit D, Mecapto or Thiuram accelerators and the like.
The antioxidants used are non-discolouring type of antioxidant and slight discolouring type of antioxidants. The Non-discolouring type of antioxidants are selected from Antioxidant BKF, Antioxidant NKF, Antioxidant MB, Antioxidant ZMB, Antioxidant NONOX SP, Antioxidant NONOX WSP, Antioxidant NONOX BROD, Antioxidant 2246, Wingstay L or Agerite White and the like.
The slight discolouring type of antioxidants are selected from Antioxidant HS or Antioxidant Nonex BROD and the like.
The optional components as softeners and fillers may also added in the subject composition, where the softeners are selected from the group comprising paraffin, paraffin wax or Stearic acid. The fillers are selected from China Clay, Mica Powder, Whiting, Lithopone, Blancfixe, Carbon Blacks or Titanium Oxide.
All the above referenced ingredients are added into the latex in the form of dispersions, emulsions or solutions in the predetermined ratio.
The inflatable bladder shell is manufactured by dipping the cleaned former into first coagulant bath to obtain a uniform film on the former. The coagulant bath is containing the components selected from the Calcium Nitrate, Calcium Chloride, Acetic acid, parting agents or carriers, water and optionally alcohol, wetting agents and defoaming agents, the former having a layer of coagulant on it is then dried. The coagulant coated former is then dipped into the tank having either a blend of compounded lattices into it or having the synthetic latex compound or natural rubber latex compound.
The latex coated former is then dried in an oven. The former is then dipped into water bath for cooling and thereafter bladder shell thus formed is stripped. The product bladder shell is then washed and dried and subjected to post curing treatment. The valve is then fitted on the neck of the bladder shell to form the bladder for the inflatable ball.